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15 Cards in this Set
- Front
- Back
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How much do enzymes speed up reactions? |
upto 1 million folds |
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Definition of an enzyme |
A protein which speeds up the rate of a chemical reaction but remains unchanged. Enzymes do not alter the equilibrium of a reaction. They are highly specific and accelerate reactions by stabilizing the transition state lower the activation energy of a reaction but energy change remains the same |
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Definition of activation energy |
The energy required to over come and reach the transition state Determines the rate of reaction |
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Mechanism of enzyme catalyse |
Provides a reaction surface (active site) stable environment (hydrophobic region) binds reactants together positions reactions for most favourable interactions weakens the bonds within reactants provides acid base catalyse + nucleophilic groups
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relationship between delta G and Rate |
Delta G= -RTlnK
rate k = deltae power -e/rt
RATE k is not dependant on equilibrium K |
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Lactate dehydeogenase enzyme example |
Converts pyruvic acid to lactic acid with reducing agent cofactor NADH2.
this occurs when muscles are over exercised |
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The active site |
Hydrophobic specifically dependant on precise fit. Amino acids present in the active site play an important role in enzyme function. Amino acids can be far apart on the primary structure but close together in the active site due to the folding of the enzyme. |
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Is the primary structure of specific enzymes the same in all humans? |
No- ps differs due to mutations through evolution but the amino acids which are crucial to the binding of an enzyme remain constant
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Definition of induced fit |
Active site on the enzyme is complementary and nearly the correct shape for the substrate. Binding of the substrate alters the shape of the enzyme to maximize intermolecular bonding.
Bonding length optimised causing the substrate to be strained causing the intramolecular bonds to be more easily broken |
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Acid/ base catalysis |
often provided by histidine amino acid as the imidzole ring is a weak base when non-ionised and an acid when ionised.
When non-ionised acts as a proton bank which is important in a hydrophobic region as not much H20 |
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Nucleophilic residues |
L-serine L-cysteine OH on serine provides for nucleophilic attack electron donors - lone pairs, ions or one pi bond |
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Mechanism for chymotrypsin |
Catalyse TRIAD of Serine, histidine and aspartase
Step 1 - hydrolysis of peptide link in amides through presence of serine. Step 2- hydroylsis of ester link |
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Why is the balance between binding forces important? |
Forces need to be strong enough to hold the substrate in place long enough for reaction to occur but the reaction is overall reversible therefore forces need to be weak enough to allow the product to depart |
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Regulation of enzyme activity |
negative feedback allosteric inhibitor binding - not similar to structure of the substrate
enzyme is usually controlled by the end product of the pathway when in high conc, binds to first enzyme as it would be noneffective if competing with product receptor site. EXTERNAL SIGNALS CAN ALSO REGULATE ENYZME ACTIVITY
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what does the signalling cascade activate? |
enzymes called protein kinases
CAUSE PHOSPHORYLATION increase enzyme activity |
